Transmissions of large commercial vehicles are divided into one main transmission part, one splitter group transmission and one range change group transmission. At the same time, modern transmissions, mainly in commercial vehicles, have one gearshifting device assisted by a pneumatic system which carries out the pneumatic gearshifts in the splitter group transmission and in the range change group transmission, while the gearshifts in the main transmission are manually carried out by a vehicle driver and, at the same time, can be assisted by the pneumatic system in an effort to be exerted.
DE 198 39 854 A1 has disclosed a gearshifting device where one power assistance device assists the driver's shifting effort. The supply of the assisting compressed air should be reduced here, for example, be admitted only, when the vehicle clutch is actuated. This requires additional valves that make a reduction possible. The disclosure of DE 198 39 854 A1 in all its contents is to be the object of this description.
DE 100 29 497 A1 has disclosed an electropneumatic gearshifting unit for a multi-ratio vehicle transmission in which a multiplicity of controlled valves shift the transmission comprised of several units while, at the same time, electronically monitored to prevent faulty functions. To that end, the valves are controlled by a central vehicle guide computer. The disclosure of DE 100 29 497 A1 in all its contents is also to be the object of this description. Modulation of the assisting force takes no place.
From DE 102 17 482, an electropneumatic gearshifting unit has finally become known where one changeover valve is provided for a vehicle transmission that comprises one main transmission manually shifted by the vehicle driver using a gearshift lever and one splitter group transmission electropneumatically shifted via valves. The gearshifts of the splitter group transmission are manually preselectable by the vehicle driver using switches on the gearshift lever. One sensor or switch detects a manual actuation of the vehicle clutch by the vehicle driver and relays the signal to an electronic control device which then opens the valves. One changeover valve is provided which, with one inlet aperture, is connected with one outlet line of the valves. The valves open every time a clutch actuation signal is present, there always opening the one of the two valves which had been preselected on the gearshift lever in the last actuation of the switches for the splitter group transmission. One outlet aperture of the changeover valves is connected, via one pneumatic line, with one pneumatic power assistance device which assists the vehicle driver when manually shifting in the main transmission. The changeover valve admits only the air supply from one of the two valves of the splitter group transmission to the pneumatic line and thus to the power assistance device while the other connecting line is shut off by the changeover valve. It is thereby prevented that the attached gearshift cylinder for the splitter group transmission receives an air supply for its two gearshifting devices. Air is to be received only by the connecting line and thus only by the part of the gearshifting cylinder that had also been preselected. It is being unimportant whether the preselection was actually effected recently by the vehicle driver or resulted in the last corresponding actuation of the switches on the gearshifting lever. For the pneumatic line and thus for the power assistance device, it is indifferent which of the two sides of the gearshifting cylinder receives air. The power assistance device should always receive air when engaged. During the gearshifting process in the main transmission, if no gearshift occurs in the splitter group transmission then, during actuation of the clutch, the same valve is again controlled which was already controlled and shifted during the last gearshift of the splitter group transmission. Thereby this valve allows air into the changeover valve and thus into the power assistance device without changing the position of the gearshifting cylinder of the splitter group transmission itself.
In mechanical transmissions having a main transmission and range change group transmission, it is possible to select the gear in the main transmission part during developing gearshift in the range change group transmission and already to apply a more or less strong manual shifting effort against a pin bolt that locks the main transmission. If the transmission has been equipped with a power assistance device, the latter is released subject to the already applied manual shifting effort, that is, a very specific pressure builds up in the power assistance device. If the gearshift is now terminated in the range change group transmission, the pin bolt again releases the gearshift in the main transmission. The power assistance device, already pressurized, acts now as a prestressed spring and accelerates the selector rod and gearshift sleeve to a high speed which results in, that if the sliding sleeve appears on the synchronizer unit, the synchronizer unit no longer locks, but grates producing loud noises. The gearshifts that produce grating noises considerably impair the duration of the synchronizer units and of all the gearshift parts. Before the failure of the transmission, this can also lead to complaints relative to the noise and to the operation of the gearshifting unit thus causing unscheduled plant stoppages.
The problem on which the invention is based is to determine the supply of assistance medium of a gearshifting device and to prevent damages without added expenses.
The problem is solved by a method having the features of claim 1 for reducing the power assistance to a gearshifting unit. Developments are object of sub-claims.